Printing plates



3,031,957 PRINTING PLATES Charles H. Van Dusen, Jr., Timber-lake, Ohio, assignor to Addressograph-Multigraph Corporation, Cleveland, Ohio, a corporation of Delaware No Drawing. Filed Jan. 27, 196i), Ser. No. 4,851 3 Claims. (Cl. 101-1492) This invention relates to planographic printing plates. This application is a continuation-in-part of my application Serial No. 636,234, filed January 25, 1957, now abondoned.

As is well known, a planographic or lithographic printing plate is one having a special surface that desirably exhibits both hydrophilic and oleophilic properties so that a greasy image can be delineated on the plate to reject water, and water next applied to the plate will be restricted to background areas surrounding the greasy image. If lithographers (oil or grease base) ink is then applied to the plate, the ink will be restricted to the aforesaid image inasmuch as the previously applied water in the background areas will repel the ink. The plate thus moistened and inked can be used in the well known offset process to produce copies that are among the finest in the graphic arts.

It is of course advantageous that the particular lithographic or planographic surface used for the plate exhibit an optimum balance between the hydrophobic characteristics of the greasy image and the hydrophilic characteristics of the background area surrounding the image, and one of the primary objects of the present invention is to achieve this balance by means of a planographic printing plate having a planographic surface comprising essentially water insoluble oxidized cellulose.

Specifically, an object of the present invention is to enable planographic printing plates to be produced in a relatively simple fashion by coating a flexible support of the plate with water insoluble oxidized cellulose.

Another object of the invention is to provide anew and improved planographic printing plate embodying a flexible support having one side or face thereof sized or treated to have high Wet strength and provided with one or more coatings of oxidized cellulose.

Another important object of the present invention is to enable planographic printing plates of the coated type to be produced easily and at relatively low cost.

Other and further objects of the present invention will be apparent from the following description which by illustration sets forth preferred embodiments of the present invention and the principles thereof and what is'n0w considered to be the best mode contemplated for applying those principles. Other embodiments of the invention embodying the same or equivalent principles may be used and changes may be made as desired by those skilled in the art without departing from the present invention.

Under the present invention, a planographic printing plate is produced having a planographic printing surface characterized essentially by water insoluble oxidized cellulose. Oxidized cellulose is prepared in a known way by treating cellulose with nitrogen tetroxide. The resultant product is soluble in aqueous alkaline solutions, and I have found that water-stable films can be prepared therefrom by rendering the aforesaid solution water insoluble. Such insolubilization of the oxidized cellulose can be produced by coating the plate with an aqueous alkaline solution of oxidized cellulose and then heating the thus coated plate to about 90 C., to insolubilize the oxidized cellulose, or, alternatively, by treatment of the coated plate with a mineralacid, such as dilute phosphoric acid, followed by heating and then washing with water. The latter form of insolubilization is preferred as will be explained hereinbelow.

Patented May 1, 1962 In producing planographic printing plates under the present invention, a solution of oxidized cellulose is first prepared by dissolving the oxidized cellulose in aqua ammonia, and the solution thus prepared is then applied as a coating to a flexible support as will be explained and the coating is rendered insoluble as described above. The flexible support may be nothing more than unbleached kraft paper, but the best results are obtained by having resort to a paper base support containing a high wet strength coating or sizing such as a paper sheet coated with insolubilized clay-casein. It is also preferable that the solution of oxidized cellulose to be applied to the flexible support be pigmented, that is, containing a suitable mineral pigment or filler. Moreover, less absorption of the oxidized cellulose coating is encountered by using a sized sheet of the kind mentioned above.

After the oxidized cellulose solution has been applied to the support, the resultant thin coating can be rendered Water insoluble simply by drying the coated support'in an over at C., but preferably insolubilization of the oxidized cellulose applied to the support is carried out by means of a weak solution of a mineral acid such as ten percent phosphoric acid (H PO and in this connection it should be noted that subsequent to treatment with mineral acidand the coated plate is rinsed in Water and then heated for about five minutes at 90 C. to obtain the finished surface. Oxidized cellulose rendered insoluble by acid treatment as set forth above exhibits better printing characteristics and image retention in comparison to insolubilization by means of heat alone, and improved results are obtained by rubbing the finished surface with a dry cotton swab or the like. Advantages of a similar order from the standpoint of printing results and image retention are attained by providing multiple layers of water insoluble oxidized cellulose, that is, by repeating the steps involved in producing a single layer coating as will be explained in more detail below. The following example of oxidized cellulose solution is sufficient to produce a single coating on a 10" x 15" sheet,

and additional amounts may be employed for multiple coatings, if desired:

Example I Material: Amount Oxidized cellulose grams 1 Aqua ammonia (28 percent) cc 10 However, a preferred composition for making the new planographic printing plates, employing a pigment filler and oxidized cellulose, is that set forth in the following example:

I have found that the pigmented composition of the foregoing Example II gives substantially better results than the unpigmented composition of Example I.

In preparing plates having multiple coatings of oxidized cellulose rendered water insoluble, the procedure is as follows, and it should be mentioned that plates prepared in this manner, especially when the finished surface is rubbed in the manner explained above, exhibit superior results in comparison to rendering the surface insoluble bytreatment with a dilute aqueous solution of a heavy metal salt such as aluminum sulface, zinc chloride or nickel sulfate. Thus, a first coating in accordance ith Example I or II above is provided on the base support, and is dried for about five minutes at 90 C. This procedure is repeated for a second coating. The exposed surface of the second coating is then uniformly treated with ten percent phosphoric acid, or a like dilute mineral acid. Following this acid treatment which effects insolubilization, the surface is rinsed in water, heated for about five minutes at 90 C. and the surface is then prefer-ably rubbed as explained above to afford the finished surface.

It will be noted that the new oxidized cellulose filmfonner is soluble in alkaline solution, but not in acid solutions, and this is advantageous in its use in forming the printing surface of planographic printing plates since such alkaline-soluble film-formers do not tend to dissolve when exposed to the action of the acidic wetting out and fountain solutions used in connection therewith in the planographic printing operation.

Hence, while I have illustrated and described preferred embodiments of the present invention, it is to be understood that'these are capable of variation and modification.

I claim:

1. A method of preparing a planographic printing plate comprising:

(a) preparing an ammoniacal solution of water insoluble oxidized cellulose;

(b)- applying a predetermined amount of said solution as a coating to a flexible base support;

(c) drying said coating for about five minutes at about C. to produce a first coated surface on said base support;

(d) repeating (b) and (c) to afford a second coated surface;

(e) treating the second coated surface with a weak solution of a mineral acid, followed by a water rinse and drying for about five minutes at about 90 C. to afford the finished printing surface.

2. A planographic printing plate prepared in accordance with claim 1 and wherein the. finished surface has been rubbed.

3. A planographic printing plate prepared in accordance with claim 1.

References Cited in the file of this patent UNITED STATES PATENTS 2,132,443 Simons Oct. 11, 1938 2,348,771 Westcott May 16, 1944 2,348,943 Westcott May 16, 1944 2,498,207 Heckel Feb. 21, 1950 2,542,784 Van Dusen Feb. 20, 1951 2,582,347 Newman Jan. 15, 1952 2,758,112 Waning Aug. 7, 1956 

1. A METHOD OF PREPARING A PLANOGRAPHIC PRINTING PLATE COMPRISING: (A) PREPARING AN AMMONIACAL SOLUTION OF WATER INSOLUBLE OXIDIZED CELLULOSE; (B) APPLYING A PREDETERMINED AMOUNT OF SAID SOLUTION AS A COATING TO A FLEXIBLE BASE SUPPORT (C) DRYING SAID COATING FOR ABOUT FIVE MINUTES AT ABOUT 90*C. TO PRODUCE A FIRST COATED SURFACE ON SAID BASE SUPPORT; (D) REPEATING (B) AND (C) TO AFFORD A SECOND COATED SURFACE; (E) TREATING THE SECOND COATED SURFACE WITH A WEAK SOLUTION OF A MINERAL ACID, FOLLOWED BY A WATER RINSE AND DRYING FOR ABOUT FIVE MINUTES AT ABOUT 90*C. TO AFFORD THE FINISHED PRINTING SURFACE. 